The present invention relates to a volume flowmeter for fluids in which a vortex is generated. It relates more particularly to a volume flowmeter of the kind comprising a chamber having a rotational symmetry about an axis, provided at its periphery with means for tangential inflow of fluid and means for axial outflow of the fluid, disposed so as to generate a vortex, and means for measuring the fluid velocity in the vortex.
There is a number of volume flowmeters designed so that there is formed therein a vortex presenting, at least locally, a rotational speed substantially proportional to the rate of flow and comprising a rotational speed sensor. Most of the existing devices have one or more of the following disadvantages: they impose on the fluid a considerable pressure drop; their response is not sufficiently proportional; they are sensitive to erratic flow fluctuations; they use mobile elements.
It is an object of the present invention to provide a device of simple construction, which comprises static elements only and is insensitive to vibrations, to shocks and to rapid flow fluctuations.
In practicing the invention, a device of the above-defined kind has a speed detector which comprises at least one transmitting thermo-element and one receiving thermo-element angularly offset about the axis and situated in a zone where the circumferential speed of the vortex is substantially proportional to the flow, means for applying short electric heating pulses to the transmitting thermo-element and means for detecting the arrival of pulse heated fluid in contact with the receiving thermo-element.
The flowmeter typically comprises a case limiting a chamber placed in the path of the fluid whose flow rate is to be measured and associated electronic means. The case may comprise, about the chamber, an annular upstream tranquilization enclosure and two downstream tranquilization enclosures into which the chamber opens axially through two converging portions. To form the vortex in the chamber, the upstream tranquilization enclosure communicates with this latter through at least one slit parallel with the axis or through holes directing the fluid in a direction having a tangential component.
The thermo-elements will generally be supported by an axial cylindrical insulating body which extends beyond the chamber and passes through the downstream tranquilization chambers. The respective diameters of the chamber and of the axial body and the distance which separates the body from the thermo-elements, advantageously formed by wires parallel to the axis, are chosen so that there is an at least approximate proportionality between the flow and the rate at which the thermo-elements are swept by the fluid.
The means may comprise a circuit for measuring the time gap between application of the electric pulses and detection by the receiving thermo-element. In this case, the pulses will generally be applied at a constant frequency, determined by a clock. Electronic means may be provided for applying an electrical heating pulse in response to the detection, the frequency of the heating pulses being then proportional to the rotational speed and therefore to the flow rate.
The invention will be better understood from reading the description which follows of particular embodiments of the device given by way of example.